1. Field of the Invention
The present invention relates generally to a pressure gauge incorporating therein liquid crystals to provide a visual indication of the pressure being measured, and more particularly pertains to a tire pressure gauge associated with a tire valve stem to provide a visual indication of the tire pressure.
2. Discussion of the Prior Art
The prior art discloses a number of different types of pressure indicators which are associated with tire valve stems to indicate the internal pressure of a tire. These pressure indicators can be constructed as an integral part of the valve stem, or can be designed as part of an attachment cap which normally threadedly engages the valve stem. Poster, U.S. Pat. No. 1,807,752, Becciani et al., U.S. Pat. No. 3,224,264 and Trinca, U.S. Pat. No. 3,177,724 are typical of the aforementioned prior art approaches to such pressure indicators. However, these prior art pressure indicators have all suffered from a major disadvantage in that they are basically mechanically operated pressure gauges, typically being dependent upon a calibrated spring or molded diaphragm to sense and react to the internal pressure of the tire.
The prior art also discloses a number of different applications for liquid crystalline materials. For example, Fergason et al., U.S. Pat. No. 3,114,836 depicts an imaging device which exhibits a color pattern on a film of liquid crystal upon focusing a heat or thermal pattern thereon. Fergason U.S. Pat. No. 3,409,404 discloses a liquid crystalline device in which variations in selective scattering of liquid crystalline materials is employed for identifying unknown materials. Williams, U.S. Pat. No. 3,322,485 utilizes a threshold characteristic of liquid crystalline material to scatter light selectively in the presence of a given electric field. Freund et al., U.S. Pat. No. 3,364,433 employs a frequency-shifting characteristic of liquid crystalline materials in the presence of an electric and/or magnetic field. None of these references, however, discloses a pressure indicator utilizing liquid crystalline materials in which the liquid crystal materials are utilized in a simple and direct fashion to obtain a visual indication of a pressure being sensed.
Sharpless U.S. Pat. No. 3,768,886 is of interest to the present invention by disclosing a variable color display which utilizes liquid crystalline materials therein and also by disclosing much material and data on stress responsive cholesteric liquid crystalline materials. In this patent selected liquid crystalline materials preferably exhibit a variable scattering or transmitive characteristic when subjected to mechanical deformation, such as occasioned by shear or flow stresses. The display device includes a liquid crystal cell which is provided with a light transmitting wall to permit viewing of the contained liquid crystalline material, and the liquid crystalline cell is associated with means for inducing mechanical stresses within the contained liquid crystalline material. This is accomplished in a variety of ways in different embodiments. For example, in one embodiment the liquid crystalline cell is constructed to permit the displacement of one wall structure thereof relative to another. In another embodiment, circulating means is associated with the cell or display device for inducing flow and attendant shear stresses within the liquid crystalline material. The display device is capable of a number of applications, for example as an aesthetic novelty, decorative wall and table top panels, back drops for stages and other illuminated areas, and numerous analogous applications.